Length exclusion in the adsorption of chain molecules on chabazite type zeolites

Daems, Inge; Singh, Ranjeet; Baron, Gino V.; Denayer, Joeri

doi:10.1039/b615661d

Cited by 34 publications

(41 citation statements)

References 11 publications

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“…It is generally accepted that the 0.38 nm apertures of CHAtype molecular sieves are small enough to categorically exclude methylalkanes from the interior surface [86]. Recent experimental studies corroborate molecular simulations indicating that CHA-type molecular sieves also contain too many of these narrow apertures per n-alkane to afford the complete adsorption of n-octane or n-decane [16,17,53,87], so that the conversion of n-octane and n-decane is indeed likely to be limited to the exterior surface and should afford an example of pore mouth and key-lock catalysis. In agreement with catalysis occurring exclusively at the small exterior surface of CHA-type molecular sieves, CHA-type sieves exhibit a dramatically lower n-octane and n-decane conversion activity than sieves with apertures large enough to accommodate reactants and products fully at their large interior surface [88][89][90].…”

Section: Catalysis On Ton-and Mtt-type Zeolites With Inactivated Extesupporting

confidence: 55%

“…If molecular sieves with ∼0.4-nm-diameter tubular channels instead of cage-containing topologies are preferred, then ATNtype sieves should be of interest [92]. It may be too early to evaluate the potential for processing alkane shape selectively at the exterior surface of zeolites, but the external zeolite surface clearly has the potential to expand the utility of concepts associated with shape-selective external surface catalysis, including cage effects [16,53], nest effects [93], pore mouth and key-lock catalysis [4][5][6][7][8][9][10][11]13,14], length-selective cracking [54], and length exclusion [87].…”

Section: Resultsmentioning

confidence: 99%

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Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Maesen

Krishna²,

Baten³

et al. 2008

Journal of Catalysis

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A critical review of the adsorption and catalysis of n-and methylalkanes demonstrates that the interior surface of TON-and MTT-type zeolites dominates both adsorption and catalysis, and that the contribution from the exterior surface is negligible. For both n-and methylalkane isomers, the experimental Henry constants at the interior TON-type zeolite surface are more than an order of magnitude greater than those at the exterior surface. Molecular simulations on exclusively interior TON-type silica surface reproduce the adsorption isotherms of n-and methylalkane isomers remarkably well and suggest that even an isomer as bulky as 2,3-dimethylpentane could have access to the interior TON-type zeolite surface. Only the reference state used in solution thermodynamics affords an equitable comparison between internal and external surface thermodynamics. It indicates that methylalkanes adsorb in a structured fashion at the exterior TON-type zeolite surface when the interior surface is inaccessible. But the entropic penalty for this organized exterior surface "pore mouth" or "key-lock" adsorption is high, so that methylalkanes prefer adsorption at the interior surface when it is accessible. We speculate that CHA-and ERI-type sieves exhibit exterior surface catalysis in long n-alkane conversion, but the database remains too small to allow investigation of the full potential of shape selectivity in exterior zeolite surface catalysis.

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Section: Catalysis On Ton-and Mtt-type Zeolites With Inactivated Extesupporting

confidence: 55%

Section: Resultsmentioning

confidence: 99%

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Maesen

Krishna²,

Baten³

et al. 2008

Journal of Catalysis

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“…Additionally, Daems et al. found that shorter alcohols such as ethanol, which can adsorb with their main carbon chain perpendicularly to the length axis of the cage, are much more efficiently packed than longer alcohols, resulting in an entropic advantage and greater affinity for the shorter chains . The combination of these kinetic and entropic effects results in a strong and unusual preference for ethanol over butanol on Si‐CHA.…”

Section: Resultsmentioning

confidence: 99%

“…More importantly, water adsorption experiments on Si‐LTA (or ITQ‐29), the pure‐silica analogue of zeolite A developed by Corma and co‐workers, indicated a very hydrophobic character with a water capacity of only 1 wt % (or 0.55 mmol g −1 ) at 20 mbar. The CHA zeolite topology on the other hand shows very specific and unusual selectivity for short chain molecules, which makes it an interesting material for the separation of short alcohols. A Si‐CHA sample, prepared by Miyamoto et al., showed hydrophobic behavior and revealed a water uptake of about 3.1 mmol g −1 at 67 mbar ( P / P 0 =0.9).…”

Section: Introductionmentioning

confidence: 99%

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

et al. 2017

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A vapor-phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanol-ethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in the vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape-selective all-silica zeolites CHA and LTA were prepared and evaluated with single-component isotherms and breakthrough experiments. These zeolites show opposite selectivities; adsorption of ethanol is favorable on all-silica CHA, whereas the LTA topology has a clear preference for butanol. The molecular sieving properties of both zeolites allow easy elimination of acetone from the mixture. The molecular interaction mechanisms are studied by density functional theory (DFT) simulations. The effects of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior are investigated. Desorption profiles are studied to maximize butanol purity and recovery. The combination of LTA with CHA-type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows butanol to be recovered in unpreceded purity and yield. A butanol purity of 99.7 mol % could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.

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“…and/or [MO 6 ] (M=V, Mn, Mo, etc.) units can be controlled 1e,l–n. In contrast, the pore sizes of MOFs, which are constructed from coordinatively bonded metal ions and organic ligands, can be controlled by the lengths and functional groups of organic ligands 1j,k.…”

mentioning

confidence: 99%

Size‐Selective Sorption of Small Organic Molecules in One‐Dimensional Channels of an Ionic Crystalline Organic–Inorganic Hybrid Compound Stabilized by π–π Interactions

2009

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The design and syntheses of porous materials such as zeolites and metal-organic frameworks (MOFs) are areas of intense research because of their unique properties in gas storage, separation, and heterogeneous catalysis. [1] Crystalline microporous zeolites show shape-selective adsorption properties because the sizes of the channel apertures formed by the covalently bonded [TO 4 ] (T= Si, Al, P, Ti, etc.) and/or [MO 6 ] (M = V, Mn, Mo, etc.) units can be controlled. [1e,l-n] In contrast, the pore sizes of MOFs, which are constructed from coordinatively bonded metal ions and organic ligands, can be controlled by the lengths and functional groups of organic ligands. [1j,k] In particular, the use of aromatic units induces p-p interactions [2] and enables the rational control of the complexation of the building units. [3] In addition, the presence of the aromatic moieties means that the resulting framework would show unique structural and guest-sorption properties. For example, the guest sorption in a Cu II dihydroxybenzoate/4,4'-bipyridine MOF [3c] causes the gliding of p-p-stacked building units, which leads to the change in the framework structure, and a Co II benzenetricarboxylate MOF [3e] separates the aromatic units from the aliphatic hydrocarbons.Trinuclear metal carboxylates have often been used as building units for the construction of MOFs, [1i, 4] which mostly contain dicarboxylates as bridging ligands to connect the trinuclear metal units, and do not show p-p interactions among the building units. [1i, 4a-c] The use of aromatic units as terminal ligands of trinuclear metal carboxylates would induce p-p interactions, which lead to the unique structural and guest sorption properties. Based on these considerations, we have used pyridine as a terminal ligand of the trinuclear metal carboxylate macrocation [Cr 3 O(OOCH) 6 (pyridine) 3 ] + in this work. Ionic crystals normally possess densely packed crystal lattices because of the strong and isotropic coulombic interaction, and thus are nonporous.

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Length exclusion in the adsorption of chain molecules on chabazite type zeolites

Abstract: In the adsorption of linear C1-C8 alkanes, alkenes and alcohols on zeolite chabazite, molecules smaller than 6.7 A are adsorbed in significant amounts, whereas longer chains are almost fully excluded from the micropores.

Cited by 34 publications

References 11 publications

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Shape-selective n-alkane hydroconversion at exterior zeolite surfaces

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity

Size‐Selective Sorption of Small Organic Molecules in One‐Dimensional Channels of an Ionic Crystalline Organic–Inorganic Hybrid Compound Stabilized by π–π Interactions

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